The present invention relates to a method and an apparatus for regenerating ion exchange resin in a water treatment tank. More specifically, the present invention relates to water treatment systems having weak acid cation type resin beds and using an existing source of carbon dioxide (CO2) for the regeneration of the resin.
In the majority of systems used to treat water intended for consumption, as in the production of beverages, the levels of various ions present in the influent water, like hardness or alkalinity are reduced. Typical ionic reductions vary depending on the quality of the feedwater source, but it is desirable to have some level of certain ionic species remaining after the treatment process. Removal of nearly all the ions present in the influent water may adversely affect the taste of the final product.
Drinking water treatment systems that make use of ion exchange technology, such as water softeners or dealkalyzers, typically include a treatment tank containing an ion exchange resin bed of bead-like granules. Ion exchange processes, which are described in further detail in U.S. Pat. No. 4,172,185, incorporated by reference herein, generally involve a reversible chemical reaction between a solid ion exchanger and an aqueous solution, where ions are transferred between the exchanger and the solution. Specifically, undesirable ions from the influent solution are exchanged on the resin, while more desirable ions are released from the resin. After a certain period of time, the ion exchange sites on the resin become saturated with the undesirable ions and must be regenerated.
It is common to use strong acid, such as sulfuric or hydrochloric acid, to most effectively regenerate the ion exchange resin following the ion exchange process. The acid, at an adequate concentration, is conventionally introduced into the tank and flows through the bed, displacing previously exchanged ions such as calcium, magnesium, and all other cationic species from the resin exchange sites. At the conclusion of regeneration, the regenerant acid is routed out to the drain, and the resin bed is rinsed with influent or other treated water prior to returning to the service phase.
A problem with these conventional regenerants is that they are best suited to larger scale commercial or industrial applications, and are not readily adaptable to smaller applications such as in the restaurant or food service setting because of regeneration safety issues. Acids at the concentrations required for regeneration are very hazardous to humans as well as corrosive to the regeneration equipment, and therefore impart safety concerns that require specialized handling. As a result, an alternative technology making use of less hazardous acids or regenerants, such citric acid and carbonic acid, is used. When using these alternate regenerants, the process is typically preformed in two separate tanks. More specifically, a separate solution tank is used to prepare a carbonic acid solution, and it is then delivered into the resin tank under pressure to regenerate the ion exchange resin. A separate regenerant tank is needed because a minimum storage time is required to generate an effective amount of dissolved carbonic acid regenerant for use with the ion exchange resin. This can take as long as several hours.
One problem with using this procedure is that the use of two tanks takes up a substantial amount of floor space, which can be a severe limitation at many facilities, as well as increasing the capital and operational cost of such systems due to multiple tanks and associated transfer equipment. In addition, the long time period required for creating the CO2 solution, and the long contact time required during the regeneration process using CO2 alone is inconvenient and increases cost.
Another disadvantage of conventional systems is that CO2 is a gas at ambient pressure and temperature, making handling more difficult and presenting a special problem in conventional systems. When preparing a CO2 solution and transferring it within the system, it must remain pressurized. Any reduction in pressure during operation will allow CO2 gas to escape from solution. This reduces the concentration delivered to the resin bed and therefore the effectiveness of the regeneration process. The regeneration is incomplete, and the capacity of the regenerated tank is reduced. The CO2 concentration delivered to the resin tank is directly dependent on the temperature and pressure of the system. This restricts the concentration of regenerant to the highest pressure the system can handle and the lowest temperature at which it can be maintained. Many potential applications of this treatment process will be limited to less than 100 psi and room temperature. Therefore, this places a severe limitation on the concentration of CO2 in the regenerant solution and the regeneration process.
Accordingly, an object of the present invention is to provide an improved method and apparatus for regenerating ion exchange resin that is more efficient in the use of space than conventional systems by reducing the number of tanks required for regeneration.
Another object of the present invention is to provide an improved method and apparatus for regenerating ion exchange resin that is more cost effective.
Yet another object of the present invention is to provide an improved method and apparatus for regenerating ion exchange resin in a shorter time period.
Still another object of the present invention is to provide an improved method and apparatus for regenerating ion exchange resin that does not require the storage of the regenerant in a regenerant tank to achieve saturation.
A further object of the present invention is to provide an improved method and apparatus for regenerating ion exchange resin that creates the regenerant in the treatment tank.
Yet a further object of the present invention is to provide for the use of non-hazardous chemicals in the regeneration process.
Still a further object of the present invention is to provide an effective regeneration process at pressures less than 100 psi and at room temperature.
Another further object of the present invention is to perform the regeneration of the ion exchange materials in such a manner as to not completely remove all of the ions from the influent water supply.
The above-listed objects are met or exceeded by the present improved method and apparatus for regenerating ion exchange resin, which features the introduction of the regenerant into the treatment tank in an opposite flow direction to the treatment flow direction. The present method and apparatus also reduces the amount of required space by introducing the regenerant directly into the tank, which also eliminates the need for a long regenerant storage time. In fact, the present invention is especially suitable for food service sites serving carbonated beverages, because the already available source of CO2 can be used to supply carbonic acid regenerant from the existing equipment to the ion exchange system. Another advantage of the present method and apparatus is that the regenerant can be created, transferred and simultaneously begin regeneration of the ion exchange resin in the treatment tank.
Efficiency of the present method for regenerating ion exchange resin is further improved by adding citric acid to the carbonic acid regenerant. It has been shown that adding citric acid to carbonic acid speeds up regeneration significantly. The addition of citric acid increases the rate at which hardness is discharged from the resin beads during the regeneration process, resulting in a dramatic reduction in the time required for a similar level of regeneration using CO2 alone. A shorter regeneration time also leads to a reduction in costs associated with higher consumption of CO2 gas and a reduction in the water used and discarded during an extended CO2 regeneration period. An advantage of the present system is that the addition of citric acid can reduce the typical regeneration time from approximately 8 hours down to 2 hours while providing the desired regeneration levels in the ion exchange resin. The handling of a solution of approximately 1% citric acid is significantly safer than handling either a more concentrated solution of a mineral acid (i.e., hydrochloric acid) or a highly compressed gas (CO2). Additionally, the citric acid delivery system is much less complex than that of a gas such as CO2. Safety in handling and reduced investment in time, capital equipment, water, and CO2 gas, as well availability work together to greatly reduce regeneration costs when citric acid is used to supplement CO2 regeneration. Testing further shows that there is a synergistic impact when CO2 and citric acid are used together in regeneration.
More specifically, the present invention provides a method for regenerating ion exchange resin in a treatment tank with a flow direction, which includes the steps of providing a supply of regenerant under pressure into the tank and introducing the regenerant into the tank in an opposite flow direction to the treatment flow direction.
In another embodiment, the present invention provides a water treatment apparatus including an ion exchange tank for generation of treated water, where the tank has an upper end and a lower end, and a treatment flow direction. An ion exchange resin is disposed in the tank for treating water. The present water treatment apparatus also includes a delivery structure for providing a supply of regenerant under pressure and an introduction structure for introducing the regenerant into the tank in an opposite flow direction to the treatment flow direction.